Most applications which use lasers require that the laser output be at a particular frequency. Many laser materials have more than one transition and, thus, can be made to lase at multiple frequencies. A typical laser includes a laser crystal contained within a resonator which is made up of two mirrors one of which is generally highly reflective and the other which is partially transmissive. In the past the selection of the proper transition of the laser was achieved by applying appropriate dielectric coatings on at least one of the mirrors to determine the reflectivity profile of the mirror and, thus, in the main reflect only the laser radiation of the desired frequency. This solution does not always work since coatings cannot always be manufactured to the proper specifications to permit reflectivity at the desired wavelength and not allow reflectivity at the frequencies of other transitions of the laser. Even if such coatings are available, they are often extremely expensive.
The problem becomes even greater in lasers where the desired frequency is one of a low gain transition of the laser and when discrimination is required against higher gain transitions.
Accordingly, it is an object of this invention to provide a laser resonator which provides improved frequency discrimination.
It is another object of this invention to provide a laser which allows discrimination against high gain transitions.